<html>
<head>
<script>
function doe() {
document.getElementById('a').style.display = 'table-column-group';
document.body.offsetHeight;
}
</script>

<style>
div::before { content:"b";}
div::after { content:"a";}
</style>
</head>

<body onload="document.body.offsetHeight; setTimeout(doe,0);">
<div style="display: table;">
  <span id="a" style="display: table-header-group; "></span>
</div>
</body>
</html>
